U.S. patent number 7,358,436 [Application Number 11/189,568] was granted by the patent office on 2008-04-15 for dual-insulated, fixed together pair of conductors.
This patent grant is currently assigned to Belden Technologies, Inc.. Invention is credited to Joseph Dellagala, Gavriel Vexler.
United States Patent |
7,358,436 |
Dellagala , et al. |
April 15, 2008 |
Dual-insulated, fixed together pair of conductors
Abstract
A high performance data cable comprises first and second
insulated conductors, each disposed in a respective first layer of
insulation and a second layer of insulation covering the first and
second insulated conductors and maintaining the first and second
insulated conductors to one another. The first and second insulated
conductors and the second layer of insulation are twisted about a
common central axis to form a twisted pair unit.
Inventors: |
Dellagala; Joseph (Shrewsbury,
MA), Vexler; Gavriel (Westmount, CA) |
Assignee: |
Belden Technologies, Inc. (St.
Louis, MO)
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Family
ID: |
35197747 |
Appl.
No.: |
11/189,568 |
Filed: |
July 26, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060021772 A1 |
Feb 2, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60591316 |
Jul 27, 2004 |
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Current U.S.
Class: |
174/27;
174/113R |
Current CPC
Class: |
H01B
11/002 (20130101); H01B 7/0216 (20130101) |
Current International
Class: |
H01B
11/00 (20060101) |
Field of
Search: |
;174/27,113R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2555670 |
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Jun 1997 |
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DE |
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1296336 |
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Aug 2002 |
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EP |
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361930 |
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Nov 1931 |
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GB |
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486970 |
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Jun 1938 |
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GB |
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5159628 |
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Jun 1993 |
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JP |
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2000-357417 |
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Dec 2000 |
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JP |
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9634400 |
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Oct 1996 |
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WO |
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Primary Examiner: Nguyen; Chau N.
Attorney, Agent or Firm: Lowrie, Lando & Anastasi,
LLP
Parent Case Text
RELATED APPLICATIONS
This application claims priority under 35 U.S.C. .sctn. 119(e) to
U.S. Provisional Application Ser. No. 60/591,316, entitled
"DUAL-INSULATED, FIXED TOGETHER PAIR OF CONDUCTORS," filed on Jul.
27, 2004, which is herein incorporated by reference in its
entirety.
Claims
What is claimed is:
1. A data cable comprising: at least one twisted pair unit
including a first insulated conductor surrounded along its length
by a first insulating layer and a second insulated conductor
surrounded along its length by a second insulating layer; and a
jacket surrounding the at least one twisted pair; wherein the at
least one twisted pair further comprises a third insulating layer
surrounding the first insulated conductor and the second insulated
conductor along their lengths to comprise first and second
dual-insulated conductors, the third insulation also fixing the
first first insulated conductor to the second dual insulated
conductor along their length; wherein a distance between a center
of the first insulated conductor and a center of the second
insulated conductor is less than a sum of a distance from the
center of the first insulated conductor to a proximate edge of the
third insulating layer and a distance from the center of the second
insulated conductor to an opposing edge of the third insulating
layer, measured along a reference line that passes through the
centers of the first and second insulating conductors wherein the
third insulating layer is formed such that the twisted pair has a
flat oval shape; and wherein the first and second insulated
conductors and the third insulating layer are twisted about a
common central axis to form the at least one twisted pair.
2. The data cable as claimed in claim 1, wherein the first
insulating layer comprises a polyolefin.
3. The data cable as claimed in claim 1, wherein the third
insulating layer comprises a fluoropolymer or fluoro-copolymer
material.
4. The data cable as claimed in claim 1, further comprising a
shield substantially surrounding the dual-insulated pair of
conductors.
5. The data cable as claimed in claim 4, wherein the shield
comprises a metallic foil.
6. The data cable as claimed in claim 5, wherein the metallic foil
comprises a polymer layer.
7. The data cable as claimed in claim 4, wherein the shield
comprises a conductive braid.
8. The data cable as claimed in claim 1, wherein the third
insulating layer is an extruded polymer.
9. The data cable as claimed in claim 8, wherein the extruded
polymer comprises flame retardant particles.
10. A data cable comprising; a twisted pair of dual-insulated
conductors comprising: a first insulated conductor insulated by a
first insulation comprising an insulating material; a second
insulated conductor insulated by a second insulation comprising the
insulating material; a third insulation insulating the first and
second insulated conductors to comprise first and second
dual-insulated conductors, the third insulation comprising: a first
portion substantially surrounding the first insulated conductor; a
second portion substantially surrounding the second insulated
conductor; a third portion joining the first and second portions;
and a jacket surrounding the twisted pair; wherein the first and
second dual insulated conductors are twisted about a common central
axis to form the twisted pair; wherein the third insulation
maintains the first and second insulated conductors with respect to
one another and is formed such that the twisted pair has a flat
oval shape; and wherein a distance between a center of the first
insulated conductor and a center of the second insulated conductor
is less than a sum of a distance from the center of the first
insulated conductor to a proximate edge of the second insulating
layer and a distance from the center of the second insulated
conductor to an opposing edge of the third insulating layer,
measured along a reference line that passes through the centers of
the first and second insulating conductors.
11. A data cable comprising: at least one twisted pair of
conductors comprising a first insulated conductor surrounded along
its length by a first insulation and a second insulated conductor
surrounded along its length by a second insulation; and a jacket
surrounding the at least one twisted pair of insulated conductors;
wherein the at least one twisted pair of conductors further
comprises a third insulation surrounding the first insulated
conductor and surrounding the second insulated conductor along
their lengths to comprise first and second dual-insulated
conductors, the third insulation being constructed to maintain the
first and second dual-insulated conductors with respect to one
another; wherein the first and second dual-insulated conductors are
twisted about a common central axis to form the at least one
twisted pair; wherein the third insulation is formed such that the
twisted pair has a flat oval shape; and wherein a distance between
a center of the first insulated conductor and a center of the
second insulated conductor is less than a sum of a distance from
the center of the first insulated conductor to a proximate edge of
the third insulation and a distance from the center of the second
insulated conductor to an opposing edge of the third insulation,
measured along a reference line that passes through the centers of
the first and second insulated conductors.
Description
FIELD OF THE INVENTION
The present invention relates to high performance data cables,
comprising dual-insulated twisted pair conductors that are fixed
together along their length.
BACKGROUND
Twisted pair cables have become the physical media of choice for
most local area networks. Twisted pair cables typically comprise a
plurality of twisted pairs of insulated conductors surrounded by a
cable jacket. The EIA/TIA 568 A Category 5 specifications (and the
associated addenda) for these cables specify transmission
performance requirements, such as maximum cross-talk, attenuation,
etc., for transmission frequencies of up to 100 MHz.
Installed transmission systems, such as networks, may operate only
at 10 Mbit/s and not use all the available bandwidth offered by
cables meeting the existing specifications. Typically the Ethernet
protocol used in many of the installed networks, employed only two
pairs of the available four and used half-duplex transmission, i.e.
one pair is transmitting while the other is receiving.
Transmission technology operating at 100 Mbit/s has been rapidly
expanding in the marketplace. Also, improved cables with
transmission characteristics exceeding the EIA/TIA 568 A Category 5
specifications (and the associated addenda) have also been
developed. Although cables may be designed to meet current
performance requirements, process variation during the manufacture
of the cable may degrade cable performance to below the required
specification. Furthermore, handling of the cable during
installation may also degrade cable performance. For these and
other reasons, cable manufacturers have developed cables with
improved performance characteristics exceeding the
requirements.
Newer data transmission technology has raised data rates above 1
Gigabit/s. This transmission technology and some of the existing
100 Mbit/s transmission technologies, when applied to twisted pair
cables, may require the use of all four pairs in a cable in
full-duplex operation (bi-directional transmission), and may
require the transmission performance of the twisted pair wire
cables to exceed the EIA/TIA 568 A Category 5 (and associated
addenda) specifications.
For many applications, it may be desirable to minimize the delay
skew or the differential in the signal velocity amongst the four
pairs in order to enable fast de-scrambling of the four bit signals
into a coherent bit sequence at the receiving end. In particular,
four pair cables usable for bi-directional transmission may need to
be high performance in order to obtain the maximum usable
bandwidth. Thus, it may also be desirable to design twisted pair
cables with low and uniform near and far end crosstalk, i.e. low
coupling of the electromagnetic fields between twisted pairs, since
crosstalk degrades cable performance. It also may be desirable to
minimize the return loss (due to impedance irregularities) of the
cable, since a high return loss may also impair transmission.
There are in the marketplace several cable designs that purport to
meet and even exceed the Category 6 specifications. One cable
design that may have gigabit capability was developed by Belden
Wire & Cable Company and is disclosed in U.S. Pat. No.
5,606,151 to Siekierka et al. Siekierka et al. discloses the
joining of the two insulated conductors in a pair by an adhesive or
by co-extruding the two insulated conductors with a joining web. In
one embodiment of the cable disclosed by Siekierka et al., each
conductor is centrally disposed within an insulation. The
insulations are integral with each other and are joined along their
lengths by a solid integral web. Siekierka et al. discloses
improved near end and far end crosstalk performance for this design
embodiment of cable. The structures also are disclosed to improve
the longitudinal impedance uniformity to less than +/-15 ohm and,
as a result, to reduce return loss of the resulting four pair
twisted cable. The observed reduction in impedance irregularities
is explained by Siekierka et al. by the fact that cyclical and
random irregularities that can be imparted in the twisted pair
during the twisting process due to differences in twisting tension
are eliminated when the conductors are first bonded together. It is
also disclosed that the cable resists deformation during handling
and installation.
U.S. Pat. No. 5,767,441, Brorein et al., discloses eliminating
impedance variations through the pre-twisting of insulated
conductors prior to twisting the insulated conductors in double
twist machines or by twisting the pairs through a single twist
process. The Brorein et al. process and others like it like have
unleashed a flood of equipment designed to impart a back-twist to
conductors of pairs in high performance cables. Brorein et al.
further disclose a flat cable structure including a plurality of
twisted pairs of conductors. However, the structure of these flat
cable designs may pose additional transmission problems, due to
inter-cable crosstalk or alien crosstalk, that is, between pairs of
different cables, due to the proximity of pairs with same twist
lays separated only by the jacket thickness, that may be difficult
to cancel electronically through DSP filtering or other
conventional techniques.
U.S. Pat. No. 5,563,377, hereinafter Arpin et al, discloses a
plenum cable comprising a jacket of minimal smoke emission material
surrounding a cable core comprising a plurality of twisted pair
conductors. Each of the conductors of the twisted pair conductors
comprises a conductor surrounded by a dual insulation, with an
inner insulating layer made from a flame retardant polyolefin and
an outer layer surrounding the inner layer formed from fluorinated
ethylene propylene (FEP).
Other cables capable of gigabit data rates may include a central
member separator to separate the individual twisted pairs from one
another to reduce crosstalk, as illustrated in FIG. 1. The use of
such a central separator 20 typically means that the twisted pairs
22a, b are closer to the cable jacket 24 than they would be without
the central separator 20. This affects the level of alien crosstalk
when two or more cables are stacked together, since the twisted
pairs of adjacent cables may be closer together than they would be
without the central separator. While the central separator 20 may
substantially reduce crosstalk, it may not eliminate impedance
irregularities. Furthermore, the insertion of a central member with
the four pairs symmetrically disposed around it may be difficult to
achieve and may slow down the manufacturing processes. In addition,
the cable diameter may be typically increased by at least 20%. The
overall cost of the cable may be also substantially increased due
to the possible additional cost of the center member and higher
jacketing material costs.
Another disadvantage of many prior art cables is illustrated in
FIG. 2. A conventional twisted pair 26 including two conductors
28a,b respectively centered in insulations 30a,b has a figure-8
shape, which has a natural groove 32. Thus, there is a tendency for
multiple twisted pairs to nest together along part of the length of
the cable, as one twisted pair 34 fits naturally into the groove 32
of another twisted pair 26. This tends to increase crosstalk in the
nested pairs. To attempt to prevent this nesting, conventional
twisted pairs may be constructed having short twist lay lengths.
However, short twist lay lengths are more difficult to achieve than
long twist lay lengths, and a fairly sophisticated twisting machine
may be required.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object to provide an improved
data cable.
One embodiment of a data cable comprises a first insulated
conductor insulated by a first insulation and a second insulated
conductor insulated by the first insulation. The first and second
insulated conductors also include a second insulation insulating
the first and second insulated conductors to comprise dual
insulated conductors. The second insulation also maintains the
first and second insulated conductors with respect to one another.
In addition, the dual insulated first and second insulated
conductors are twisted about a common central axis to form a
twisted pair of conductors within the cable.
Another embodiment of a data cable comprises at least one twisted
pair of conductors including a first insulated conductor surrounded
along its length by a first insulation and a second insulated
conductor surrounded along its length by a second insulation. The
twisted pair of conductors also includes a third insulation
surrounding the first insulated conductor and the second insulated
conductor along their lengths to comprise dual-insulated
conductors. The third insulation also fixes the first dual
insulated conductor to the second dual insulated conductor along
their length.
Another embodiment of a data cable comprises at least one twisted
pair of conductors comprising a first insulated conductor
surrounded along its length by a first insulation and a second
insulated conductor surrounded along its length by a second
insulation. The at least one twisted pair of conductors also
includes a third insulation surrounding the first insulated
conductor and surrounding the second insulated conductor along
their lengths to comprise dual-insulated conductors. The first and
second insulated conductors are fixed together along their lengths
with a bonding agent.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, in which like elements are represented by like
numerals:
FIG. 1 is a cross-sectional illustration of a prior art cable
containing a central separating member;
FIG. 2 is an illustration of nesting among twisted pairs according
to the prior art;
FIG. 3 illustrates a cross-sectional view one embodiment of a
dual-insulated, fixed together conductors;
FIG. 4 illustrates a cross-sectional view of another embodiment of
dual-insulated, fixed-together conductors;
FIG. 5 is an illustration of a cross-section of one embodiment of a
cable comprising a plurality of dual-insulated, fixed together
twisted pairs of conductors;
FIG. 6 is an illustration of a cross-section of another embodiment
of a cable comprising dual-insulated, fixed together twisted pairs
of insulated conductors;
FIG. 7 is a cross-section view of yet another embodiment of a cable
comprising dual-insulated, fixed together twisted pairs of
insulated conductors
FIG. 8 is a cross-sectional view of another example of a twisted
pair of conductors;
FIG. 9 is a cross-sectional illustration of two adjacent twisted
pairs of conductors;
FIG. 10 is an illustration of two adjacent twisted pairs according
to the prior art; and
FIG. 11 is an illustration of a dual-insulated, fixed together
twisted pair unit having a secondary insulating layer formed with
an indentation.
DETAILED DESCRIPTION
Various illustrative embodiments and aspects thereof will now be
described in detail. The present invention will be more easily
understood after reading the following description with reference
to the accompanying figures.
Referring to FIG. 3, there is illustrated one embodiment of a
twisted pair of conductors that can be used, for example, in high
frequency applications. The two conductors 35, 36 can be any of
solid, stranded, hollow or any other configuration known to those
of skill in the art. For example, the conductors may be a solid
metal, a plurality of metal strands, a fiberglass conductor, a
layered metal or any combination thereof. Each conductor, 35, 36 is
substantially insulated along its length by a respective first
insulating layer 37, 38. In one embodiment, each of the conductors
35, 36 is disposed centrally within the corresponding first
insulating layer 37, 38.
Each insulated conductor 35, 36, insulated by respective first
insulations 37, 38, is also insulated along their length by a
second insulation 39 to comprise dual-insulated conductors along
their lengths. The insulated conductors are also formed so that
they are joined along their respective lengths in any suitable
manner known to those of skill in the art. For example, for the
embodiment illustrated in FIG. 3, the first and second insulated
conductors are joined together along their respective lengths by
the insulating layer 39, such that the second insulating layer
fixes the first and second insulating conductors together. In other
words, the second insulating layer 39 is formed, such as for
example extruded, so that it joins the first and second insulated
conductors.
FIG. 4 illustrates another embodiment of a dual-insulated, fixed
together twisted pair. It is to be appreciated that like components
are illustrated with like reference numbers. In this embodiment
first and second insulated conductors 35, 36, insulated by
respective first insulating layers 37, 38, are substantially
insulated by additional second respective insulating layers 41, 43.
The insulated conductors are also fixed together along their length
by any appropriate bonding agent known to those of skill in the
art. For example, the bonding agent may be any adhesive used in the
industry. It is to be appreciated that in the embodiment of FIG. 4,
the adhesive 45 is illustrated disproportionate to that which may
typically be used, for purposes of illustration, and that the
figure is not drawn to scale.
It is to be appreciated that the embodiments of FIG. 3 and FIG. 4
can be manufactured according to known manufacturing techniques
used in the industry. For example, the insulated conductors 35, 36
are prepared by extruding insulating layers 37, 38 and 39 over the
conductors 35, 36 and then adhering the insulated conductors
together, for example, by causing the insulating material 39 to
come together for each of the insulating conductors while the
insulating material 39 is at an elevated temperature, prior to
cooling, to provide a joined cable without the use of an adhesive.
Alternatively, the insulated conductors 35, 36 are extruded with
respective insulations 37 41 and 38 43, and brought together during
the manufacturing process, for example, just after the extrusion of
the insulating layers and fixed together with an adhesive or
bonding agent 45 as illustrated in FIG. 4.
Accordingly, one embodiment of a method of manufacture of the
twisted pairs of insulated conductors 35, 36 comprises extruding
the first insulation material 37, 38 over the respective
conductors, followed by extruding the second insulation material 39
over the insulated conductors 35, 36, and adhering the insulated
conductors with the dual insulation layers together by contacting
the first and second insulated conductors while the second
insulation layer is at an elevated temperature, such that the
insulated conductors affixed together when cooled. Alternatively,
the method may also comprise introducing a bonding agent 45 between
the dual-insulated conductors to affix the dual-insulated
conductors together. The affixed insulated conductors can then be
twisted at a desired twist lay to provide twisted conductors having
a desired twist lay.
One embodiment of a cable comprising dual insulated conductors
fixed to each other and twisted to form twisted pairs comprises
high copper alloy conductors 35, 36, for example, that are 24
standard wire gauge (AWG). The first insulation layer 37, 38
insulating each conductor comprises a flame retardant polyolefin,
such as polyethylene. The second insulation layer 39 insulating the
insulation layers 37, 38 comprises fluorinated ethylene propylene
(FEP). The first insulating layer 37, 38 and the outer insulating
layer 39 of FEP may have the same or different thicknesses. The
cable may also comprise a jacket (not illustrated in FIGS. 3-4),
for example of minimal smoke emission such as a polyvinyl chloride
or a Halar fluoropolymer. In addition, the cable may also include
at least one shield that substantially surrounds the twisted pairs
of conductors and that is substantially enclosed by the jacket. For
example, the shield may comprise a braid such as a braid of a high
copper alloy or a metallic foil such as a copper alloy layer on an
insulating base layer, that can be wrapped around the twisted pairs
of conductors.
It is to be appreciated that although one embodiment of a cable
comprising dual insulated, fixed together twisted pairs of
conductors than can makeup a core of a cable has been described,
various modifications to the conductors, the insulating materials,
the shielding materials and the cable materials can be made and are
contemplated by this disclosure. For example, the conductors 35, 36
may be constructed of any material used in the industry, and can
be, for example, solid or stranded, a copper or copper alloy, a
metal coated substrate, a silver, aluminum, a steel, alloys of
different materials or a combination of any of the above. In
addition, the first insulating material and the second insulating
materials may be any insulating materials used for the insulation
of conductors, such as polyvinyl chloride, polyethylene,
polypropylene, flouropolymers, flouro-copolymers, cross-linked
polyethylene and the like. In addition, the diameter of each of the
conductors, 35, 36, can be, for example, anywhere in the AWG range
between 18 to 40 AG. Further, the insulation thickness of the first
insulating layers 37, 38 can be anywhere in a range from 0.001
inches to 0.030 inches. In addition, the insulating range of the
second insulating layer 39, 41, 43 can be anywhere in a range from
0.001 inches to 0.030 inches. Further, the cable core can comprise
any number of twisted pairs of insulated conductors.
Some of the advantages of the cable comprising the dual-insulated,
fixed-together conductors include, for example, that each twisted
pair of conductors has a center-to-center distance that does not
vary by more than about <0.0005 to 0.001 inches. This results
from the fixing of the conductors together such that the twisting
of the conductors does not result in the variations discussed above
with respect to the prior art. In addition, another advantage of
such embodiments of the cable of this disclosure is that the dual
insulated, fixed-together, twisted pairs of conductors can be
pulled apart relatively easily, for example, after an initial cut,
so that the cables can be pulled apart, stripped, and terminated in
any standard connector in the industry. Another advantage of the
dual insulated, fixed-together, conductors is that the dual
insulation layer is left intact even with the pulling apart of the
insulated conductors. Still another advantage of such embodiments
of such a cable is that the dual insulated conductors can be
separated, for example, for at least an inch from the end of a
cable to facilitate the terminating a connector, but the remainder
of the cable need not separated, and can remain intact with the
desired twist lay.
It is to be appreciated that the cables described herein may be
data, communications, or other high-performance cables and
typically comprise a plurality of dual-insulated, fixed-together
twisted pairs of conductors. Referring to FIG. 5, there is
illustrated one embodiment of a cable comprising such
dual-insulated, fixed-together insulated conductors. Each twisted
pair includes two individual conductors 35, 36 that are
substantially insulated by a first respective insulating layer 37,
38, and which are substantially insulated by a second insulated
layer 39. The dual-insulated conductors are fixed together along
their length as described above. The fixed-together, dual-insulated
conductors are twisted about a common axis to form a twisted pair
unit 44. The plurality of twisted pairs units are surrounded by a
cable jacket 102 that may define the shape of the cable. The cable
may be, for example, a substantially round cable 48, as illustrated
in FIG. 5, or the twisted pairs of conductors may be disposed, for
example, side-by-side in a flat cable 50, as illustrated in FIG. 6.
However, it is to be understood that the invention is not limited
in this regard and the cable may have any other shape used in the
industry. The twisted pairs of conductors may be disposed in
alternate arrangements within the cable jacket, as desired. For
example a + shaped filler 20 as illustrated in FIG. 1 may be
provided in the cable core.
Referring to FIG. 7, there is illustrated another embodiment of a
cable 51 comprising a plurality of dual-insulated, fixed-together
twisted pairs of insulated conductors according to aspects of the
invention. In this embodiment, the plurality of twisted pairs 44
may be disposed in a substantially side-by-side arrangement, as
shown, each twisted pair 44 being disposed within its own channel
46 within a jacket 104 of the cable. In one example, the channels
46 may be formed by inwardly extending protrusions 49 of the jacket
104. However, it is to be appreciated that the channels 46 may also
be formed by other suitable methods and structures, for example,
the cable 51 may comprise a separator (not shown) that may be
disposed between the twisted pairs 44 to provide the channels 46.
In the illustrated example, the jacket 104 has a substantially
crescent shape that defines the overall shape of the cable.
However, it is to be appreciated that the jacket 104 is not limited
to a crescent shape and may have various other shapes and
structures as known and used in the art. For example, the cable may
have a flat shape such as illustrated in FIG. 6, a round shape as
shown in FIG. 5, and the like. As shown in FIG. 7, each twisted
pair includes two individual conductors 35, 36 that are
substantially insulated by a first respective insulating layer 37,
38, and which are substantially insulated by a second insulating
layer 39. It is further to be appreciated that the second
insulating layer 39 of each conductor of the twisted pair may be
fixed together by any of the methods and means described
herein.
According to another embodiment of a cable, illustrated in FIG. 8,
a twisted pair of insulated conductors 52 includes conductors
54a,b, each conductor individually insulated with a corresponding
insulation 56a,b, to form insulated conductors. Both insulated
conductors 54a,b are covered by a secondary insulating layer 58, to
form the pair of conductors 52. The two conductors of the pair, and
the surrounding insulations, are twisted about a common central
axis to form the twisted pair of conductors 52. The insulation
56a,b surrounding conductors 54a,b may provide rigidity to the pair
of conductors, and prevent deformation of the pair of conductors
during twisting. The insulation may also control the distance
between the conductors 54a,b and thus control the impedance of the
cable. The insulation 56a,b is typically a solid layer to perform
the functions described above, but may also be foamed in some
applications.
According to one example, the spacing 60 between the centers of the
conductors 54a,b is less than the sum of the distances 62, 64 from
the centers of conductors 54a,b to the edges of the insulating
layer 58, measured along a reference line 66 that passes through
the centers the conductors 54a,b. Stated another way, the
conductors 54a,b may be separated by a distance 60 that is smaller
than the distance 68 separating conductors 54a and 54b in adjacent
pairs, when cables are adjacently arranged as illustrated in FIG.
9. By contrast, in the known art, illustrated in FIG. 10, the
twisted pairs of conductors are centered in tubular insulation
having a circular cross-section, and the separation 70 between the
two conductors in a pair is substantially equal to the separation
72 between conductors in adjacent pairs.
An advantage to a pair of conductors as illustrated in FIG. 8 is
that, while the impedance of individual pairs (e.g., FIG. 5, 44;
FIG. 6, 44) of the proposed cable is equivalent to that of a
conventional cable having identical conductor separation, the
minimum separation distance (FIG. 9, 68) between adjacent pairs of
one embodiment of the proposed cable exceeds the norm in a
conventional cable. The higher separation between conductors of
adjacent pairs produces tangible electrical performance
improvements, such as reduced crosstalk between adjacent twisted
pairs and lower signal attenuation. These reductions contribute to
an improved signal-to-noise performance of the proposed cable.
In one embodiment as illustrated in FIGS. 8-9, the secondary
insulation layer 58 may be uniformly formed such that the twisted
pair unit has a flat oval shape. According to another embodiment, a
twisted pair of conductors 74 may comprise a secondary insulation
layer 76 that may be formed with an indentation 78, as illustrated
in FIG. 11. In the illustrated example, the indentation is
substantially centered between the two conductors, although it need
not be. A cable comprising twisted pairs of conductors 74 has the
same improved electrical performance characteristics as described
above.
A cable comprising twisted pairs of conductors having any of the
structure described above may have a number of advantages. The
second insulation layer provides uniformity to the twisted pair of
conductors, and facilitates twisting since there is no need to
control the location and tension in two conductors. Rather, the two
conductors of the pair are held in place within the pair unit by
the second insulating layer, and thus only the single pair unit
need be controlled. A less sophisticated twisting machine may
therefore be used to perform the twisting, which may reduce the
cost of the cable. A cable containing these twisted pairs may also
be easier to terminate than a cable containing conventional twisted
pairs. One reason for this is that the secondary insulating layer
holds each conductor of the twisted pair in a known location
relative to the other conductor and to the twisted pair unit.
Therefore, there is no need to locate and/or control the tension or
twist in two conductors, as is the case for conventional twisted
pairs.
One mechanical characteristic of elastomers is their capacity to
undergo relatively high strain in the elastic domain under
relatively low mechanical stress and to achieve complete recovery
following the release of the stress. Conversely, for high elastic
modulus materials, there is typically a small strain domain where
the material behaves elastically under relatively high stress;
beyond that domain, high modulus materials may deform permanently
or plastically.
According to one embodiment, the cable described herein takes
advantage of the presence of an elastomer as the secondary
insulating layer to create, during the twisting process and pair
unit assembly, a structure that may be mechanically pre-stressed
and may resist further deformations. For example, the elastomer
layer may be readily deformed to effect a deformation that may be
still in the elastic domain following the twisting process, and may
resist further deformations. The elastomer layer may also cushion
variations in the tension generated in the pair unit during
spooling, which may result in better spooling and may facilitate
twisting of the pair unit. The elastomer layer may also absorb
variations in tension generated during twisting, thereby limiting
dimensional variations to the thickness of the elastomer layer,
which may help to stabilize the impedance of the cable.
Yet another advantage of a cable comprising some embodiments of the
twisted pair units described above is that the flat oval shape of
the twisted pair unit resists nesting, thereby helping to reduce
crosstalk between twisted pair units in the cable. As discussed
above, conventional twisted pairs typically have a figure-of-8
shape that has a wide natural groove that tends to cause nesting of
the multiple twisted pairs in a cable (see FIG. 2). By comparison,
the flat, oval shape of the twisted pair unit (FIG. 8, 52)
described above resists nesting as the secondary insulating layer
may be formed without a groove. The fact that the twisted pair
units resist nesting also allows the twisted pair units to have a
longer twist lay length which may be beneficial in terms of cost,
and may allow a less sophisticated twisting machine to be used to
perform the twisting.
As discussed above, the oval shape and eccentricity of the twisted
pair units of the proposed cable described above reduces crosstalk
between twisted pairs within the cable. Therefore, the proposed
cable may have acceptably low levels of crosstalk without using a
central separator. This is advantageous since, as discussed above,
a central separator may increase the size, cost, and manufacturing
complexity of a cable, and may cause increased alien crosstalk.
Furthermore, for cables having an equal jacket thickness and
tightness, the twisted pair units of the proposed design may be
located closer to the center of the cable than they would be were a
central separator used, meaning that they are inherently further
away from twisted pairs in an adjacent cable. This may tend to
reduce alien crosstalk between stacked cables, compared with
conventional cables having a central separator. Alternatively, the
outer diameter of the proposed cable may be reduced compared with a
conventional cable having a central separator, since the twisted
pairs may be more closely spaced within the cable. This may be
advantageous in terms of cost and space required for installation
of the cable.
According to another embodiment, the outer insulating layer may be
used as a carrier for color, flame retardant or smoke retardant
additives. This may be particularly advantageous for cables that
are desired to be used in fire retardant applications. The
insulating layer may incorporate inorganic flame retardant
particles, or may be itself a flame retardant polymer. In yet
another example, the outer layer of insulation may be foamed in
order to reduce the signal attenuation of a twisted pair unit, and
thus of a cable comprising such twisted pair units, since foaming
may lower the dielectric constant of the layer by increasing the
amount of air present in the layer. Foaming may also increase the
compressibility of the outer insulation layer.
According to one embodiment, the cable comprising the
dual-insulated, fixed together twisted pair may be an unshielded
cable, as is illustrated in FIG. 5. In this example, the cable
includes a plurality of twisted pair units 44, typically four,
wrapped in a cable jacket 102 with no shielding around either the
pair units themselves, or the cable as a whole. It is to be
appreciated that while the illustrated cable has four twisted pairs
in an exemplary configuration, the proposed cable is not so
limited. Furthermore, the twisted pair units may have any secondary
insulating layer as described herein.
In another embodiment, the cable may be a shielded cable, as is
also illustrated in FIG. 5. A shielded cable can include a single
shield or screen 103, that surrounds all of a plurality of twisted
pair units 104, underneath the cable jacket 102. Typical prior art
shielded cables may need larger insulated conductors in order to
ensure that the shield is further away from the center wire of the
conductors, so as to prevent the shield from interfering with the
conductors, causing crosstalk. A shielded cable may be made from
any of the twisted pairs units described above. An additional
advantage of constructing a shielded cable using any of the twisted
pair units as disclosed herein is that the twisted pair units may
be inherently more rigid that conventional twisted pairs, and thus
may tend to maintain their shape and facilitate the shield 103
being wrapped around them. The shield may be conductive, such as a
conductive braid or a metallic foil, and may be supported by a
polymer film. A drain wire may also be included in the cable jacket
and may be connected to the shield.
According to yet another embodiment, the cable may be a fully
shielded cable wherein each twisted pair unit 44 is also
individually shielded with a shield (not illustrated), and an
overall shield 103 is additionally applied underneath the cable
jacket 102, and surrounding all of the plurality of twisted pair
units. Fully shielded cables may be standard for CAT7 cables.
Either or both of the individual shields and the additional overall
shield may be conductive, and may be, for example, a conductive
braid or metallic foil. The shields may be supported by polymer
films.
Having thus described various embodiments of proposed cables, and
aspects thereof, modifications and variations may be apparent to
those of ordinary skill in the art. For example, it is to be
appreciated that while exemplary embodiments of various shielded
and unshielded cables have been illustrated to have the
dual-insulated, fixed together twisted pair units arranged in a
particular configuration, the proposed cables are not so limited.
The cables may include any number of such twisted pair units that
may be arranged in any configuration within the cable jacket.
Additionally, such twisted pair units may have any described
secondary insulating layer. Furthermore, the cables need not be
round and may be flat or have another outer shape as desired. The
cables may also include a central separating member to separate
individual twisted pair units from one another. Such and other
modifications and variations are intended to be covered by this
disclosure, and the scope of the invention is determined by proper
construction of the appended claims, and their equivalents.
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